Descriptions

The use of CIPC (isopropyl N-(3-chlorophenyl) carbamate) to
control dodder (Cuscuta spp.) in alfalfa is an established practice. A
rate of six pounds per acre applied to moist soil has given good dodder
control lasting from four to six weeks.
The purpose of this study was to determine the effect of CIPC
vapors on dodder seedlings. In order to obtain a relatively high percent
germination of dodder seeds, the seeds were scarified with concentrated
sulfuric acid and planted in sterile soil. Since dodder is a
parasitic plant it was necessary to find a suitable host plant. Alfalfa
and carrots were used in initial experiments and toothpicks were substituted
for the host plants in later experiments. It was found that
dodder seedlings would wrap around toothpicks and haustoria would
develop. Control of dodder seedlings was measured by counting the
number of wrapped or attached dodder seedlings on a suitable host.
Dodder seedlings were exposed to CIPC vapors in a closed plastic vapor trap system. Twenty percent granular CIPC at six
pounds per acre was applied to moist soil within the vapor trap. Exposure
of dodder seedlings to CIPC vapors for 2, 4, 8, 16, 32, and 64
hours indicated that at least 16 hours exposure was necessary to prevent
seedlings from wrapping. A similar experiment was carried out
using CIPC at six pounds per acre on dry soil. Complete control of
dodder seedlings was obtained in each experiment.
Dodder seedlings were grown in 12 x 75 mm test tubes. They
were then exposed to CIPC vapors released from CIPC granules in
the open greenhouse. The test tubes provided assurance that all contact
between CIPC and the dodder must have been as a vapor. In all
cases the seedlings failed to wrap around the toothpicks.
Data from a field experiment using the test tube method and alfalfa
as a host showed positive dodder control as a result of CIPC
vapor toxicity.
An attempt was made to determine whether CIPC in the soil
solution or CIPC vapors were most active in controlling dodder seedlings.
In all cases seedlings were isolated from CIPC in soil solution.
The vapors released did prevent wrapping of dodder seedlings on the
toothpicks. A suitable method was not found which would assure only
exposure of dodder seedlings to CIPC in the aqueous form.
The evidence collected shows that CIPC vapors are important
in the control of dodder seedlings.